The present invention pertains to multi-site ventricular pacing systems, and particularly Bi-Ventricular and AV synchronous cardiac pacing systems that pace and sense in at least one atrial heart chamber and deliver ventricular pacing pulses to right ventricular (RV) and left ventricular (LV) sites separated by a Vxe2x80x94V delay for treatment of heart failure, and particularly to measuring QRS duration as a heart failure parameter and optimizing the AV delay and/or Vxe2x80x94V delay to enhance ventricular filling and cardiac output as a function of QRS duration.
Congestive heart failure (CHF) is defined generally as the inability of the heart to deliver enough blood, i.e., to supply sufficient cardiac output, to the peripheral tissues to meet metabolic demands. Frequently CBF is manifested by left ventricular dysfunction (LVD), but it can have a variety of sources. For example, CHF patients may have any one of several different conduction defects. The natural electrical activation system through the heart involves sequential events starting with the sino-atrial (SA) node, and continuing through the atrial conduction pathways of Bachmann""s bundle and intemodal tracts at the atrial level, followed by the atrio-ventricular (AV) node, Common Bundle of His, right and left bundle branches, and final distribution to the distal myocardial terminals via the Purkinje fiber network. A common type of intra-atrial conduction defect is known as intra-atrial block (IAB), a condition where the atrial activation is delayed in getting from the right atrium to the left atrium. In left bundle branch block (LBBB) and right bundle branch block (RBBB), the activation signals are not conducted in a normal fashion along the right or left bundle branches respectively. Thus, in a patient with bundle branch block, the activation of the ventricle is slowed, and the QRS is seen to widen due to the increased time for the activation to traverse the conduction path. For example, in a patient with LBBB, the delay in the excitation from the RV to the LV can be as high as 120 to 150 ms.
In diseased hearts exhibiting LVD and CHF, cardiac depolarizations that naturally occur in one upper or lower heart chamber are not conducted in a timely fashion either within the heart chamber or to the other upper or lower heart chamber. In such cases, the right and left heart chambers do not contract in optimum synchrony with each other, and cardiac output suffers due to the conduction defects. In addition, spontaneous depolarizations of the left atrium or left ventricle occur at ectopic foci in these left heart chambers, and the natural activation sequence is grossly disturbed. In such cases, cardiac output deteriorates because the contractions of the right and left heart chambers are not synchronized sufficiently to eject blood therefrom. Furthermore, significant conduction disturbances between the right and left atria can result in left atrial flutter or fibrillation.
More particularly, as described in commonly assigned U.S. Pat. No. 6,129,744, LVD and other forms of heart failure are manifested by reduced ejection fraction from the left ventricle thereby reducing stroke volume and pulmonary edema limiting the patient""s ability to exercise. Patients suffering from LVD are also known to have elevated levels of catecholamines at rest because the body is attempting to increase cardiac output that induce a higher resting heart rate. In addition, the QT interval for such a patient is affected by the catecholamine level and thus has a changed pattern during exercise as well. These patients have a decreased QT response, or smaller change in QT, during exercise, such that the QT interval shortening during exercise is smaller than that found normally. Although QT interval is influenced independently by heart rate alone, as well as by exercise and catecholemines, it is not known to what extent each of these factors or both are responsible for the changed QT response to exercise in LVD patients. However, it is known that patients suffering LVD clearly have a different pattern of QT interval shortening during exercise. Moreover, the changed conductive patterns or a heart in heart failure are manifested by other changes in the PQRST waveforms, particularly an abnormally wide or long duration of the ventricular depolarization signal, or QRS.
It has been proposed that various conduction disturbances involving both bradycardia and tachycardia of a heart chamber could benefit from pacing pulses applied at multiple electrode sites positioned in or about a single heart chamber or in the right and left heart chambers in synchrony with a depolarization which has been sensed at least one of the electrode sites. It is believed that atrial and left ventricular cardiac output can be significantly improved when left and right chamber synchrony is restored, particularly in patients suffering from dilated cardiomyopathy, LVD and CHF.
A number of proposals have been advanced for providing pacing therapies to alleviate heart failure conditions and restore synchronous depolarization and contraction of a single heart chamber or right and left, upper and lower, heart chambers as described in detail in the above referenced ""744 patent and in commonly assigned U.S. Pat. Nos. 5,403,356, 5,797,970, 5,902,324, and 6,070,100 and in U.S. Pat. Nos. 5,720,768 and 5,792,203. The proposals appearing in U.S. Pat. Nos. 3,937,226, 4,088,140, 4,548,203, 4,458,677, 4,332,259 are summarized in U.S. Pat. Nos. 4,928,688 and 5,674,259. The advantages of providing sensing at pace/sense electrodes located in both the right and left heart chambers is addressed in the ""688 and ""259 patents, as well as in U.S. Pat. Nos. 4,354,497, 5,174,289, 5,267,560, 5,514,161, and 5,584,867.
The medical literature also discloses a number of approaches of providing bi-atrial and/or bi-ventricular pacing as set forth in: Daubert et al., xe2x80x9cPermanent Dual Atrium Pacing in Major Intra-atrial Conduction Blocks: A Four Years Experiencexe2x80x9d, PACE (Vol. 16, Part II, NASPE Abstract 141, p.885, April 1993); Daubert et al., xe2x80x9cPermanent Left Ventricular Pacing With Transvenous Leads Inserted Into The Coronary Veinsxe2x80x9d, PACE (Vol. 21, Part II, pp. 239-245, January 1998); Cazeau et al., xe2x80x9cFour Chamber Pacing in Dilated Cardiomyopathyxe2x80x9d, PACE (Vol. 17, Part II, pp. 1974-1979, November 1994); and Daubert et al., xe2x80x9cRenewal of Permanent Left Atrial Pacing via the Coronary Sinusxe2x80x9d, PACE (Vol. 15, Part II, NASPE Abstract 255, p. 572, April 1992).
In the above-referenced ""324 patent, an AV synchronous pacing system is disclosed providing three or four heart chamber pacing through pace/sense electrodes located in or adjacent one or both of the right and left atrial heart chambers and in or adjacent to the right and left ventricular heart chambers. During an AV delay and during a V-A escape interval, a non-refractory ventricular sense event detected at either the right or left ventricular pace/sense electrodes starts a conduction delay window (CDW) timer. A ventricular pace pulse is delivered to the other of the left or right ventricular pace/sense electrodes at the time-out of the CDW if a ventricular sense event is not detected at that site while the CDW times out.
The above-referenced ""744 patent discloses a rate responsive, bi-ventricular pacemaker having one or more sensors for sensing a parameter indicative of the physiologic need for cardiac output, and for pacing the patient on demand between a lower rate limit (LRL) and an upper rate limit (URL). In a specific embodiment, the pacemaker determines QT interval, and stores data representative of changes in QT interval as a function of paced heart rate and/or the patient""s spontaneous lower rate when at rest. Variations in the correlation of QT interval and heart rate, and/or variations in patient lower rate at rest are processed to provide a time trend, or profile, from which a determination is made as to whether or not LVD is indicated. In alternate embodiments, other data derived from cardiac signals is processed and stored, e.g., QRS duration, T-wave amplitude, etc. A change in the variation of T-wave amplitude with respect to exercise, and consequent heart rate, can be easily measured and tracked in a QT rate responsive pacemaker, or any pacemaker adapted to sense and recover the T-waves. Likewise, as noted above, changes in QRS duration (width) and/or morphology may also be detected and tracked for detection of a trend. Trends in this data are periodically evaluated, e.g., on a daily basis, and stored for downloading to an external programmer for deriving an indication of LVD, or onset or progression of LVD or for automatic initiation of a treatment response signals.
In the ""744 patent, an algorithm for automatically adjusting the rate responsive parameters, i.e., the correlation function between QT and desired rate is suitably performed on a daily basis. The pacemaker measures a slope of the correlation function at the LRL, and adjusts the QT-rate function between LRL and URL accordingly as disclosed in commonly assigned U.S. Pat. No. 4,972,834. If such changes are stored and analyzed for a trend, progress toward LVD can be indicated. Likewise, if it is found that the patient heart rate is not dropped to the programmed LRL during nighttime, such that the spontaneous lower rate has had an upward progression, this trend can also be used as an indicator of the onset of LVD.
As asserted in the ""744 patent, these functions can be performed in an implanted monitor solely dedicated to detection and storage of cardiac data and processing of such data to provide an indication of LVD when interrogated. In a more preferred embodiment, a rate responsive pacemaker system is disclosed that can pace and sense in any combination or all of the four cardiac chambers. The treatment response upon an indication of onset of LVD has a number of embodiments, including changing the rate response function; changing physiologic sensor blending for dual or plural sensor rate responsive pacemakers; initiating three or four chamber pacing to achieve improved left heart response, e.g., synchronous ventricular pacing and/or other multi-chamber sequential pacing; and providing for a measured release of an appropriate drug for treating the LVD. In yet another disclosed embodiment, the pacemaker is implanted with software for carrying out normal dual chamber pacing, but the software can be upgraded by programmer downloading to provide different pacing functions, or to function as a three or four chamber pacemaker, along with utilization of an additional lead or leads for delivering stimulus pulses to the left heart chambers.
In commonly assigned U.S. Pat. No. 5,749,906, a dual chamber pacing system, is disclosed that continually adjusts the AV delay so as to maintain optimal ventricular pacing for therapy of patients having cardiomyopathy. The QRS duration of paced ventricular events is monitored, and analyzed to determine if the paced ventricular event is a fusion beat with an intrinsic ventricular depolarization. If fusion beat frequency criteria established for the patient are met, then the AV delay is shortened incrementally so that the ventricular pace pulse is delivered earlier, and fewer fusion beats occur.
Chronically collected data from patients with progressive LVD or other types of heart failure is needed so that the treating cardiologist can properly and accurately chart the progression, determine the nature of the heart failure, and be able to implement the optimal treatment in a timely fashion. There is also a substantial need in the art for a pacemaker or other implantable medical device (IMD) incorporating three or four channel pacing having the capacity to optimize the AV delay and the Vxe2x80x94V pacing delay for pacing the RV and LV to treat the changing patient condition.
In view of the above need, the present invention provides a system and method for monitoring patient cardiac signals and processing such signals within IMD to provide data from which the onset or progression of heart failure can be determined, particularly the QRS duration as measured during a paced depolarization of the heart, and optimizing synchronous pacing delay parameters to minimize the measured QRS duration.
The present invention is implemented in a wide variety of ways. In the broadest context, the present invention pertains to cardiac pacing systems that pace or sense ventricular events (V-EVENT) at or deliver a first ventricular pace (V-PACE1) pulse to a first ventricular site and deliver a ventricular pace (V-PACE2) pulse to a second ventricular site spaced from the first ventricular site after a Vxe2x80x94V delay from the V-EVENT or V-PACE1. A measurement of the cardiac depolarization QRS duration is initiated upon delivery of the V-PACE2. The QRS duration can be retained in IMD memory for retrieval and analysis at a later time or transmitted to a remote external medical device in real time. A series of QRS duration times can be measured and processed to determine maximum, minimum and average QRS duration that are stored in memory.
The QRS duration is preferably measured from a selected pair of sense electrodes located remote from the first and second ventricular sites.
The present invention is preferably implemented in a bi-ventricular pacing system wherein the first ventricular site is one of an RV site or an LV site and the second ventricular site is the other of the RV or LV site, whereby pacing pulses V-PACE1 and V-PACE2 are delivered in the RV-LV sequence or the LV-RV sequence. The V-PACE1 can be delivered either upon the time-out of a pacing escape interval or upon the V-EVENT occurring prior to time-out of the escape interval. The QRS duration can be measured from the V-PACE2 pulse following time-out of the Vxe2x80x94V delay timed from a V-EVENT (a VS marker), a V-PACE1 delivered upon a V-EVENT (a VS/VP marker) or a V-PACE1 (a VP marker).
The present invention is also preferably implemented in a three or four chamber pacing system wherein pacing and sensing at one or both of an RA site and an LA site are provided. Bi-ventricular pacing in the LV and RV is provided, wherein V-PACE1 may be delivered to one of the LV site or RV site after time-out of a SAV delay from an atrial event (A-EVENT) sensed at one of the RA or LA sites or a PAV delay an atrial pace pulse delivered to one of the RA or LA sites. V-PACE2 is delivered to the other of the LV site or RV site after time-out of the Vxe2x80x94V delay.
Accordingly, this invention provides a system and method for monitoring the QRS duration, processing such signals to provide data from which the onset or progression of heart failure is determined, and adjusting synchronous pacing delay parameters including SAV delay and/or PAV delay and/or Vxe2x80x94V delay to enhance cardiac output as a function of QRS duration. The SAV delay and/or the PAV delay and/or the Vxe2x80x94V delay can be varied from the prevailing delays as a function of measured QRS duration so as to minimize the width of the QRS complex.
In accordance with one aspect of the present invention, the optimal Vxe2x80x94V delay and optionally the optimal PAV delay or SAV delay or the combination of the same that minimizes the measured QRS duration and maximizes mechanical heart performance is determined. In one variation of this aspect of the invention, the SAV delay and/or PAV delay and/or Vxe2x80x94V delay providing the minimum QRS duration is derived by successively applying incremented or decremented ones of the SAV delay, PAV delay and/or Vxe2x80x94V delay, deriving a QRS_DURSAMPLE value at each adjusted delay, comparing the set of N derived QRS_DURSAMPLE values to determine the minimum QRS_DURSAMPLE value, and setting the SAV delay, PAV delay and/or Vxe2x80x94V delay to the SAV delay, PAV delay and/or Vxe2x80x94V delay that provides the minimum QRS13 DURSAMPLE value.
Another manner of determining the values of the SAV delay, PAV delay, and/or Vxe2x80x94V delay that provide a minimal QRS duration (QRS13 DURMIN) following delivery of the V-PACE2 involves measuring the QRS13 DURSAMPLE values after a change in one or more of the Vxe2x80x94V delay, SAV delay, and PAV delay are compared with the preceding or prior measured QRS13 DURSAMPLE value to determine if the change has decreased the QRS duration. An additional change in the same direction (increasing or decreasing the parameter duration) is made if the prior change does decrease the QRS duration. But, if the change results in an increase in the measured QRS duration, then the change direction is reversed to repeat the measurement of the QRS duration using the prior parameter value. A rest period of a number of heart cycles or a time period is provided between each change in a Vxe2x80x94V delay, SAV delay, and PAV delay parameter value to allow the heart to acclimate to the change.
These methods can be first practiced by the physician in the initial post-implant telemetry session to derive and store in IMD memory the SAV delay, PAV delay and/or Vxe2x80x94V delay that affords the shortest QRS duration that is also retained in memory as the QRS DURRF value. The methods are then performed at a programmed time of day preferably when the patient is at rest and the patient""s heart rate is low and stable. The derived SAV delay, PAV delay and/or Vxe2x80x94V delay that affords the shortest QRS duration are then employed until the next programmed time of day or other event criteria are met.
This summary of the invention has been presented here simply to point out some of the ways that the invention overcomes difficulties presented in the prior art and to distinguish the invention from the prior art and is not intended to operate in any manner as a limitation on the interpretation of claims that are presented initially in the patent application and that are ultimately granted.